We have shown that addition of mitogens to quiescent 3T3 cells results in a rapid increase in the phosphorylation of a membrane protein with a molecular weight of 33,000 daltons (33K protein). We propose to determine whether stimulation of phosphorylation of the 33K protein by mitogens can be correlated with the effect of these mitogens on DNA synthesis. To accomplish this we shall investigate the effect of several mitogens under varied conditions on both DNA synthesis and membrane phosphorylation in 3T3 cells. In addition to these studies, we shall further investigate the intracellular localization of the 33K protein by subcellular fractionation of 32P-labeled mitogen-stimulated cells.